Method for fueling an engine at start

ABSTRACT

A method for improving starting of an engine that may be repeatedly stopped and started is presented. In one example, fuel injection timing is selectively adjusted based on engine stop position and amount of time the engine is stopped. The method may improve engine starting and lower engine noise.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/293,002, filed on Nov. 9, 2011, now U.S. Pat. No. 8,423,271,the entire contents of which are incorporated herein by reference forall purposes.

FIELD

The present description relates to a method and system for improvingrestarting of an engine. The method may be particularly useful forengines that are stopped automatically and then restarted automatically.

BACKGROUND AND SUMMARY

An engine of a vehicle may be automatically stopped and restarted duringperiods of time when vehicle motion is not requested or desired by thevehicle operator. By stopping the engine, it may be possible to conservefuel that would otherwise be consumed if the engine were allowed tocontinue to operate. However, restarting the engine can increase engineemissions if an undesirable amount of fuel is inducted to enginecylinders. Further, where the engine is a port fueled engine, it may bemore difficult to control fuel amounts entering engine cylinders sincefuel can only enter the cylinders during times when intake valves of thecylinders are open. Consequently, it may take longer to start an enginethat is port injected. One way of decreasing engine starting time of aport fueled engine is to inject fuel to engine cylinders when valves ofthe cylinders are open during an engine restart. However, injecting fuelduring a time when an intake valves are open can reduce fuelvaporization and may cause fuel to impinge on cylinder walls, therebyincreasing engine emissions.

The inventors herein have recognized the above-mentioned disadvantagesand have developed a method for starting an engine, comprising: duringan engine start and after an engine start request, selectively injectingfuel to a port of a single cylinder of the engine having an open intakevalve at a time fuel is injected to the port; and injecting fuel to eachremaining cylinder of the engine at a time when an intake valve of acylinder receiving fuel is closed.

By injecting fuel to a single cylinder during intake valve opening ofthe cylinder, it may be possible to reduce engine emissions and improveengine starting. In particular, after the first cylinder is fueled at atime when its intake valve is open, fuel may be injected to remainingengine cylinders during timing when valves of the remaining cylindersare closed. Open valve injection to the one cylinder allows the cylinderto combust fuel earlier than if fuel injection started at only at closedvalve timing. However, the cylinders that subsequently receive fuel canreceive fuel when intake valves of the cylinders are closed so that fuelvaporization is improved and so that cylinder wall wetting may bedecreased in the remaining cylinders at start. Thus, in one example,only one cylinder is fueled to promote early combustion while allremaining cylinders are fueled to reduce emissions and promote fuelvaporization.

In some examples, the open intake valve injection may be selectivelyapplied. For example, during some conditions open intake valve injectionmay occur while during other conditions open intake valve injection isnot permitted. Specifically, open intake valve injection is permittedwhen the intake valve opening duration from engine stop position tointake valve closing time (e.g. a remaining amount of intake valveopening duration) is greater than a predetermined number of crankshaftdegrees. Selectively injecting fuel based on valve opening timing canreduce engine emissions by reducing the amount of excess fuel in thecylinder port for subsequent ignition events.

The present description may provide several advantages. Specifically,the approach may improve engine emissions by improving cylinder mixturesat engine start time. In addition, the approach may reduce engine noiseduring starting by helping to ensure that a desired amount of fuel is ina cylinder when combustion is initiated in the cylinder. Further, theapproach may reduce excess fueling of engine cylinders during a start soas to reduce engine fuel consumption.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages described herein will be more fully understood by readingan example of an embodiment, referred to herein as the DetailedDescription, when taken alone or with reference to the drawings, where:

FIG. 1 is a schematic diagram of an engine;

FIGS. 2-5 show example simulated engine starting sequences; and

FIG. 6 is a flowchart of an example engine starting method.

DETAILED DESCRIPTION

The present description is related to engine fueling duringautomatically starting an engine. In one non-limiting example, theengine may be configured as illustrated in FIG. 1. Engine starting maybe performed according to the sequences described by FIGS. 2-5. Themethod of FIG. 6 may be executed via controller instructions in a systemas shown in FIG. 1 to provide the engine starting sequences shown inFIGS. 2-5.

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is showncommunicating with intake manifold 44 and exhaust manifold 48 viarespective intake valve 52 and exhaust valve 54. Each intake and exhaustvalve may be operated by an intake cam 51 and an exhaust cam 53.Alternatively, one or more of the intake and exhaust valves may beoperated by an electromechanically controlled valve coil and armatureassembly. The position of intake cam 51 may be determined by intake camsensor 55. The position of exhaust cam 53 may be determined by exhaustcam sensor 57.

Fuel injector 66 is shown positioned to inject fuel into an intake port95 of cylinder 30, which is known to those skilled in the art as portinjection. Alternatively, fuel may be injected to combustion chamber 30,which is known to those skilled in the art as direct injection. Fuelinjector 66 delivers liquid fuel in proportion to the pulse width ofsignal FPW from controller 12. Fuel is delivered to fuel injector 66 bya fuel system (not shown) including a fuel tank, fuel pump, and fuelrail (not shown). Fuel injector 66 is supplied operating current fromdriver 68 which responds to controller 12. In addition, intake manifold44 is shown communicating with optional electronic throttle 62 whichadjusts a position of throttle plate 64 to control air flow from airintake 42 to intake manifold 44. In one example, a low pressure directinjection system may be used, where fuel pressure can be raised toapproximately 20-30 bar. Alternatively, a high pressure, dual stage,fuel system may be used to generate higher fuel pressures.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of catalytic converter 70. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a position sensor134 coupled to an accelerator pedal 130 for sensing force applied byfoot 132; a measurement of engine manifold pressure (MAP) from pressuresensor 122 coupled to intake manifold 44; an engine position sensor froma Hall effect sensor 118 sensing crankshaft 40 position; a measurementof air mass entering the engine from sensor 120; and a measurement ofthrottle position from sensor 58. Barometric pressure may also be sensed(sensor not shown) for processing by controller 12. In a preferredaspect of the present description, engine position sensor 118 produces apredetermined number of equally spaced pulses every revolution of thecrankshaft from which engine speed (RPM) can be determined.

In some embodiments, the engine may be coupled to an electricmotor/battery system in a hybrid vehicle. The hybrid vehicle may have aparallel configuration, series configuration, or variation orcombinations thereof. Further, in some embodiments, other engineconfigurations may be employed, for example a diesel engine.

Engine 10 may be rotated via engine starter 99 during engine starting.Engine starter 99 may be electrically or hydraulically driven. Enginestarter includes pinion 98 which can selectively engage engine 10 via aflywheel (not shown). Controller 12 can automatically selectively rotateengine 10 to start engine 10 after controller 12 automatically stopsengine 10. Further, engine starter 99 may be engaged directly via arequest via a vehicle operator or driver.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion. During the expansion stroke, the expanding gases pushpiston 36 back to BDC. Crankshaft 40 converts piston movement into arotational torque of the rotary shaft. Finally, during the exhauststroke, the exhaust valve 54 opens to release the combusted air-fuelmixture to exhaust manifold 48 and the piston returns to TDC. Note thatthe above is shown merely as an example, and that intake and exhaustvalve opening and/or closing timings may vary, such as to providepositive or negative valve overlap, late intake valve closing, orvarious other examples.

Referring to FIG. 2, an example plot of a simulated engine startsequence by the method of FIG. 6 is shown. The illustrated sequencerepresents a start of a non-limiting four cylinder four cycle engine.The order of cylinder events during engine stopping and starting maydepart from the illustration of FIG. 1 without departing from the scopeof disclosure. For example, fuel may be injected to cylinder numberthree instead of cylinder number one and the first combustion event maybe initiated in cylinder number three as opposed to cylinder number onewithout departing from the scope of the description.

In this example, a four cycle, four cylinder engine having a firingorder of 1-3-4-2 is shown automatically stopping and starting. Timebegins on the left side of the plot and increases to the right side ofthe plot. In this example, the vertical markers between cylinderposition traces CYL. 1-4, represent top-dead-center orbottom-dead-center for the respective cylinder strokes. In addition,there are 180 crankshaft degrees between each vertical marker. It shouldalso be noted that the amount of time between strokes of a cylinder mayvary such that the scale of time may expand and contract between theleft side and right side of FIG. 2, but the angular interval betweencylinder events remains constant. Thus, the X axis for each of thesubplots of cylinder events is relative to engine position, except wherethe engine is stopped as indicated by the SS line brakes and labels. Thecylinder strokes are abbreviated as shown where CMP is an abbreviationfor compression stroke and EXP is an abbreviation for expansion stroke.Further, exhaust and intake strokes are abbreviated with EXH and INTrespectively.

Asterisks such as indicated at 200 provide timing of spark events duringthe sequence shown. Spark is shown being provided during the compressionstroke of the cylinders but spark may also be provided early during theexpansion stroke. Injector nozzles with spray such as indicated at 220,222, 224, and 226 provide timing of fuel injection events for port fuelinjectors associated with the cylinder where the injector is shown. Forexample, at 220, fuel is injected to the intake port of cylinder numberone. Intake valve opening timings are shown as wide lines at 204, 206,208, and 210. In this example, the intake valve opening time extendsfrom during a late portion of the exhaust stroke to an early portion ofthe compression stroke. However, alternative valve timings of longer orshorter duration are within the scope of this description. Additionally,the valve timings illustrated may be advanced or retarded more than isshown in some examples.

Open intake valve injection occurs in FIG. 2 and FIGS. 3-5 when a centerof an injector nozzle is shown above a wide line such as 204 thatrepresents intake valve opening time. Closed intake valve injectionoccurs in FIG. 2 and FIGS. 3-5 when a center of an injector nozzle isshown above an area without a wide line such as 204.

The first plot from the top of the figure represents position ofcylinder number one. And, in particular, the stroke of cylinder numberone as the engine crankshaft is rotated from torque provided by astarter motor or combustion within the engine. Strokes of cylindernumber one are labeled according to the engine position. For example,cylinder number one is shown on a compression stroke before time T₀.After T₀, the engine continues to rotate and cylinder number one entersan expansion stroke where gases in the cylinder apply force to move thepiston away from the cylinder head. Subsequently, the cylinder entersexhaust and intake strokes. The cylinder cycle for cylinder number onerepeats after the engine rotates through a complete cycle. For a fourstroke engine, a cylinder cycle may be 720°, the same crankshaftinterval for a complete cycle of the engine.

The second cylinder position trace from the top of the figure representsthe position and stroke for cylinder number three. Similarly, positiontraces for cylinder numbers four and two are provided in the third andfourth plots from the top of FIG. 2. The fifth plot from the top of FIG.2 represents engine speed during the automatic engine starting andstopping sequence.

To the left of T₀, the engine is rotating at idle speed, for example. Attime T₀, an engine controller (e.g., 12 from FIG. 1) requests anautomatic engine stop. In particular, the engine stop request is madewithout an operator directly requesting an engine stop via an enginestop command or request (e.g., via a pushbutton or switch). In oneexample, the automatic engine stop may be generated when vehicle speedreaches zero while the driver actuates a brake without actuating anaccelerator. The engine may be stopped by ceasing to inject fuel and/orprovide spark to engine cylinders.

In the example of FIG. 2, the engine is stopped in an orderly mannerafter the engine stop request at time T₀. In particular, enginecylinders that contained an air-fuel mixture prior to the engine stoprequest are allowed to combust the air-fuel mixture. Further, in enginecylinders where fuel injection was started (e.g., cylinder number four)fuel injection is completed and the air-fuel mixture in the cylinder iscombusted as indicated by the spark events after time T₀ and before timeT₂.

At time T₁, engine speed approaches zero and the controller judges thatcylinder one is to receive a fuel charge so that combustion may beinitiated first in cylinder number one during a subsequent enginerestart after engine stop. The controller may select a particularcylinder to receive fuel without sparking during an engine stop based onengine position and engine speed. For example, if engine speed is lessthan 100 RPM and engine cylinder number one is in an intake stroke aboutto enter a compression stroke, cylinder number one may be selected orjudged to be a cylinder for a first combustion event during a subsequentengine restart. In this way, the controller provides fuel to a cylinderduring engine stop so that the fuel may be used to start the engine uponrequest at a later time.

In the example of FIG. 2, cylinder number one is selected to receivefuel before an engine stop and fuel is injected at time T₁. Since theengine is port injected, the selected cylinder has to be a cylinder thatwill open an intake valve to induct the injected fuel, and it is desiredthat the fuel is not expelled to the exhaust before the engine isstopped. In other words, the cylinder to receive fuel for initiating afirst combustion event during a subsequent engine start receives fuelfrom a port fuel injector during an open or closed intake valve timeperiod, inducts the fuel to the cylinder via opening the intake valve,and if the engine stops as planned, the fuel is not expelled to theexhaust system via opening an exhaust valve of the cylinder.

At time T₂, the engine ceases to rotate and is stopped. The engine comesto rest at a position early in a compression stroke of cylinder numberone. Although it may be desirable to retain the last amount of fuelinjected in a cylinder by having closed intake and exhaust valves, theengine may stop at a location as shown in FIG. 1 where the intake valveis at least partially open do to engine friction and air amounts trappedin engine cylinders.

The engine remains stopped from time T₂ to time T₃. Accordingly, theintake valves for cylinders 1-4 remain in their respective states. Inparticular, intake valves for cylinder numbers one and three remainopen.

At time T₃, an automatic engine start is requested. In one example, theautomatic engine restart may be initiated when a vehicle operatorreleases a vehicle brake. If the engine stop time is short,substantially all fuel injected to cylinder number one may remain incylinder number one. Consequently, the engine may be restarted withoutinjecting additional fuel to cylinder number one, and cylinder numberone may be the first cylinder to combust an air fuel mixture sinceengine stop during a subsequent engine restart. However, when enginestop time is greater than a threshold time, and when the intake valve isopen for longer than a threshold amount of crankshaft rotation asindicated at 250 (e.g., equal to or more than 30 crankshaft degrees), anadditional amount of fuel may be injected as shown to the cylinder tolast receive fuel (e.g., cylinder number one) so that the cylinder is afirst cylinder to combust an air-fuel mixture during a subsequent enginerestart.

Thus, the system of FIG. 1 provides for a system for starting an engine,comprising: an engine including a plurality of cylinders, each of theplurality of cylinders including intake and exhaust valves; a group offuel injectors supplying fuel to ports of the plurality of cylinders;and a controller including instructions to stop the engine via stoppingfuel and spark delivered to the plurality of cylinders, except for oneor more cylinders that receive fuel without spark to aid in enginerestarting, the controller including further instructions to selectivelycombust the fuel in the one or more cylinders that receive fuel withoutspark during a restart of the engine, the fuel in the one or morecylinders not combusted when a stop time of the engine exceeds athreshold amount of time. In this way, a more robust engine start may beperformed by the system.

The system also includes further instructions for combusting fuel in theone or more cylinders when the stop time of the engine is less than athreshold amount of time without injecting additional fuel. The systemalso includes where the fuel in the one or more cylinders that receivefuel without spark is trapped via closing the intake and exhaust valves.The system further includes instructions to inject fuel to one cylinderof the engine that does not receive fuel without spark before enginestop while a valve of the one cylinder that does not receive fuelwithout spark before engine stop is open before a first combustion eventin the one cylinder that does not receive fuel without spark beforeengine stop. The system also includes further instructions to injectfuel to each remaining cylinder of the engine at a time when an intakevalve of a cylinder receiving fuel is closed. In some examples, thesystem includes where the controller includes instructions forautomatically stopping and starting the engine.

In the example of FIG. 2, fuel is injected to cylinder number one whilethe intake valve of cylinder one is open in response to a request torestart the engine. In some examples, the fuel may be injected beforethe starter is engaged to allow the fuel to enter the cylinder while thevalve is open. If the intake valve of the cylinder last to receive fuelduring an engine stop sequence is in a position where the intake valveis open for less than a predetermined threshold amount of crankshaftrotation (e.g., less than 30 crankshaft degrees), then the engine may berestarted in an alternative manner as shown in FIG. 3. The engine startsto rotate under power of an engine starter at the time right of time T₃.Further, the fuel injected at times T₁ and T₃ is combusted at a timeshortly after time T₄ as indicated by the asterisk above the cylindernumber one plot.

At time T₄, fuel is injected to cylinders numbered three and four. Inparticular, fuel is injected to cylinder number three while the intakevalve of cylinder number three is open. Fuel is injected to cylindernumber four while the intake valve of cylinder number four is closed.Injecting fuel to cylinder number three while its intake valve is openallows continuity of combustion in the engine firing order. However, ifdesired, the injection of fuel to cylinder number three may be omittedin some examples so that fuel is only injected to a single cylinderhaving an open valve before injection is transitioned to injecting fuelon closed valves for all engine cylinders. Injecting fuel to a singlecylinder for only the first combustion event of the cylinder during anengine restart may reduce hydrocarbon emissions and cylinder wallwetting.

After time T₄, the engine runs up to idle speed and fuel is injected toall engine cylinders when intake valves of the respective cylinders areclosed. Injecting fuel when an intake valve is closed can improve fueland air mixing and reduce cylinder wall wetting by fuel. Thus, engineemissions may be reduced via injecting on closed intake valves afterinjecting fuel to a single cylinder during time of an intake valve beingopen.

Referring now to FIG. 3, a sequence similar to the sequence of FIG. 2 isshown. The plots of FIG. 3 are similar to those of FIG. 2, therefore arepeat of some elements common to the figures is omitted and differencesbetween the figures are described.

Spark timing of ignition supplied to each cylinder is indicated byasterisks as shown at 300. Intake valve open timing for cylinder numberone is indicated by the wide lines at 304. Similarly, intake valveopening timings for cylinders numbered two through four are indicates at306, 308, and 310. Port fuel injection timing is shown as indicated bythe nozzles at 320, 322, 324, and 326.

At time T₀, the engine is rotating at idle speed when an engine stoprequest is made. The engine is stopped in an orderly manner by ceasingfuel injection and spark to engine cylinders. Specifically, cylindersnumbered one, three, and four combust air fuel mixtures that wereinducted before the engine stop request at time T₀ as indicated byasterisks. The engine speed falls as combustion ceases.

At time T₁, fuel is injected to cylinder number one with the intent totrap the fuel in the cylinder to promote rapid engine restarting. Theengine continues to rotate and comes to a stop at time T₂ where theintake valve of cylinder number one is open, but where the intake valveof cylinder number one will be open for fewer crankshaft degrees whenthe engine is rotated after the engine start request at time T₃ ascompared to the number of crankshaft degrees shown in FIG. 2. The numberof crankshaft degrees that the intake valve of cylinder number one isopen during engine cranking is illustrated at 350. Further, the numberof crankshaft degrees that cylinder number one is open during enginecranking is less than a threshold amount where additional fuel may beinjected to cylinder number one. Therefore, injection of additional fuelto cylinder number one is omitted when the amount of time the engine isstopped exceeds a threshold. If the engine is stopped for a period oftime less than a threshold, combustion may be initiated in cylindernumber one via a spark during the compression stroke of cylinder numberone after the request to start the engine.

At time T₃, a request to automatically start the engine is made. In thisexample, the time that the engine is stopped (e.g., between times T₂ andT₃) exceeds a threshold amount and the intake valve is open for lessthan a threshold amount of crankshaft degrees after engine rotationbegins. Consequently, injection of additional fuel to the port ofcylinder number one during the time the intake valve of cylinder numberone is open since engine stop is omitted in the sequence of FIG. 3.Omitting fuel injection to cylinder number one during the period ofshort intake valve opening time can reduce the possibility of overfueling cylinder number one during a subsequent cylinder cycle becausethe second intake event for cylinder number one would not induct twofuel charges. Instead of a small fraction of fuel entering the cylinderand a larger portion of fuel staying in the cylinder port afterinjecting on an open intake valve in response to a request to start,fuel may be injected for the first time since engine stop upon a secondopening of the intake valve of cylinder number one. In this way, thecylinder number one receives only a single fuel charge rather than twofuel charges during the second cycle of cylinder number one. The enginebegins to rotate at time T₃.

Between time T₃ and T₄, fuel is injected during open intake valve timingfor cylinder number three. Further, fuel is injected during closedintake valve timing for cylinder number four. Thus, after engine stop,fuel is injected to a single cylinder while the cylinder's intake valveis open and then fuel is injected to the respective other cylinderssequentially in order of combustion during times when intake valves ofthe respective cylinder are closed. For example, the fuel injectorsupplying fuel to the port of cylinder number two injects fuel during aperiod when the intake valve of cylinder number two is closed.

After time T₄, fuel is injected to engine cylinders during closed intakevalve conditions. In addition, combustion is initiated in each cylinderduring the respective compression strokes of each cylinder asillustrated. Further, engine speed continues to increase until theengine reaches idle speed.

Referring now to FIG. 4, a sequence similar to the sequence of FIGS. 2and 3 is shown. The plots of FIG. 4 are similar to those of FIG. 2,therefore a repeat of some elements common to the figures is omitted anddifferences between the figures are described.

Spark timing of ignition supplied to each cylinder is indicated byasterisks as shown at 400. Intake valve open timing for cylinder numberone is indicated by the wide lines at 404. Similarly, intake valveopening timings for cylinders numbered two through four are indicates at406, 408, and 410. Port fuel injection timing is shown as indicated bythe nozzles at 420, 422, 424, and 426.

At time T₀, the engine is rotating at idle speed when an engine stoprequest is made. The engine is stopped in an orderly manner by ceasingfuel injection and spark to engine cylinders. Specifically, cylindersnumbered one, three, and four combust air-fuel mixtures that wereinducted before the engine stop request at time T₀ as indicated byasterisks. The engine speed falls as combustion ceases.

At time T₁, fuel is injected to cylinder number one with the intent totrap the fuel in the cylinder to promote rapid engine restarting. Theengine continues to rotate and comes to a stop at time T₂ where theintake valve of cylinder number one is closed and where the fuelinjected at time T₁ is trapped in the cylinder. None of the othercylinder are shown holding fuel injected during the engine stopprocedure. However, in some examples, fuel may be injected to two ormore cylinders without igniting the mixtures during an engine stop sothat an air-fuel mixture may be combusted in the cylinders withoutinjecting additional fuel to the cylinders during the first twocombustion events during a subsequent engine start. Such an injectionsequence may be particularly useful for engines having more than fourcylinders.

The engine stops at time T₂ and the intake valve of cylinder number oneis closed trapping an air-fuel mixture in the cylinder. In the exampleof FIG. 4, cylinder number one stops at the intended time where anair-fuel mixture is trapped in the cylinder to facilitate enginestarting. Trapping an air-fuel mixture in a cylinder may be particularlyuseful in stop/start vehicles where the engine is expected to stop andstart with higher frequency. The trapped air-fuel mixture may be appliedto start the engine without injecting additional fuel to the cylinderwith the trapped air-fuel mixture. In particular, starting may beinitiated by simply supplying a spark to the cylinder storing theair-fuel mixture. Thus, engine cranking time may be reduced.

In this example, the time that the engine is stopped is between time T₂and T₃. The time between T₂ and T₃ represents an amount of time lessthan a threshold amount of time where the air-fuel mixture stored incylinder number one is substantially disturbed during the engine stopperiod.

At time T₃, an automatic engine start request is made. Since theair-fuel mixture in cylinder number one is not disturbed by air seepingout or crankcase gases seeping into the cylinder, an ignition spark issupplied to cylinder number one after the engine is rotated withoutinjecting additional fuel to cylinder number one during the firstcylinder cycle since engine stop. Fuel is also injected to cylindernumbers three and four at time T₃. Specifically, fuel is injected duringopen intake valve timing for cylinder number three and fuel is injectedduring closed intake valve timing for cylinder number four. Fuel isshown being injected during subsequent cylinder cycles for each cylinderduring closed intake valve conditions. Thus, in the example of FIG. 4, afirst combustion event is initiated via a single spark, followed by asingle open valve injection of fuel into the port of a single cylinder,followed by closed valve injections to the remaining cylinders. Such asequence may reduce engine emissions and shorten engine starting time bycombusting air-fuel mixtures in each cylinder entering a compressionstroke from start. In other examples, fuel may be injected so as to trapthe air-fuel mixture during in the expansion or intake stroke where itmay be subsequently combusted during an engine start. Such an option isalso available for the sequences illustrated in FIGS. 2, 3, and 5.

Referring now to FIG. 5, a sequence similar to the sequence of FIGS. 2,3 and 4 is shown. The plots of FIG. 5 are similar to those of FIG. 2,therefore a repeat of some elements common to the figures is omitted anddifferences between the figures are described.

Spark timing of ignition supplied to each cylinder is indicated byasterisks as shown at 500. Intake valve open timing for cylinder numberone is indicated by the wide lines at 504. Similarly, intake valveopening timings for cylinders numbered two through four are indicates at506, 508, and 510. Port fuel injection timing is shown as indicated bythe nozzles at 520, 522, 524, and 526.

At time T₀, the engine is rotating at idle speed when an engine stoprequest is made. The engine is stopped in an orderly manner by ceasingfuel injection and spark to engine cylinders. Specifically, cylindersnumbered one, three, and four combust air-fuel mixtures that wereinducted before the engine stop request at time T₀ as indicated byasterisks. The engine speed falls as combustion ceases.

At time T₁, fuel is injected to cylinder number one with the intent totrap the fuel in the cylinder to promote rapid engine restarting. Theengine continues to rotate and stops at time T₂ where the intake valveof cylinder number one is closed and where the fuel injected at time T₁is trapped in the cylinder. None of the other cylinders are shownholding fuel injected during the engine stop procedure. However, in someexamples, fuel may be injected to two or more cylinders without ignitingthe mixtures during an engine stop so that an air-fuel mixture may becombusted in the cylinders without injecting additional fuel to thecylinders during the first two combustion events during a subsequentengine start. Such an injection sequence may be particularly useful forengines having more than four cylinders.

The engine stops at time T₂ and the intake valve of cylinder number oneis closed trapping an air-fuel mixture in the cylinder. In the exampleof FIG. 5, cylinder number one stops at the intended time where anair-fuel mixture is trapped in the cylinder to facilitate enginestarting. The trapped air-fuel mixture may be applied to start theengine without injecting additional fuel to the cylinder with thetrapped air-fuel mixture. In particular, starting may be initiated bysimply supplying a spark to the cylinder storing the air-fuel mixture.Thus, engine cranking time may be reduced.

In this example, the time that the engine is stopped is between time T₂and T₃. The time between T₂ and T₃ represents an amount of time greaterthan a threshold amount of time where the air-fuel mixture stored incylinder number one is substantially disturbed during the engine stopperiod. Rather, in the example of FIG. 5, the air-fuel mixture trappedin the cylinder may be altered via seeping air and crankcases gases tothe extent that combusting the cylinder mixture may not be desirable.For example, the cylinder mixture may have less capacity to generatetorque, thereby leading to engine noise and vibration. Therefore, it maybe desirable to skip combustion in the cylinder that received fuelduring an engine stopping sequence for one cylinder cycle. The fuelejected by the cylinder can be oxidized by catalyst in the vehicleexhaust system. Further, the ejected fuel may act to rebalance chemistryin the catalyst from lean conditions caused by air being pumped throughthe catalyst during engine stop.

At time T₃, an automatic engine start request is made. Since theair-fuel mixture in cylinder number one is disturbed by air seeping outor crankcase gases seeping into the cylinder, an ignition spark is notsupplied to cylinder number one after the engine is rotated withoutinjecting additional fuel to cylinder number one during the firstcylinder cycle since engine stop. However, fuel is injected to cylindernumbers three and four at time T₃. Specifically, fuel is injected duringopen intake valve timing for cylinder number three and fuel is injectedduring closed intake valve timing for cylinder number four. Fuel isshown being injected during subsequent cylinder cycles for each cylinderduring closed intake valve conditions. Thus, in the example of FIG. 5, afirst combustion event is avoided in the cylinder where an air-fuelmixture was held during engine stop. Further, a single open valveinjection of fuel into the port of a single cylinder is followed byclosed valve injections to the remaining cylinders and the engine isstarted. Such a sequence may reduce engine emissions when the timebetween engine stopping and starting exceeds a threshold amount of time.

Thus, as illustrated in FIGS. 2-5, fuel may be injected to one or morecylinders without combusting the fuel during an engine stop for thepurpose of assisting engine restart. However, the engine may stop inpositions where intake valves of the cylinders receiving fuel during anengine stop sequence are open or closed. Further, the time that anair-fuel mixture is trapped in a cylinder of a start/stop vehicle mayvary such that if the air-fuel is held longer than a threshold amount oftime, combustion of the contents of the cylinder with the trappedair-fuel mixture can degrade engine starting. Therefore, the sequencesillustrated in FIGS. 2-4 may be useful for improving engine starting.

It should also be noted that engine position may be determined at thetime of engine stop by tracking engine position as spark and fuel aredeactivated. In one example, engine position is determined and stored tomemory for retrieval during the next engine start when the engine issubstantially stopped. In another example, engine position may bedetermined at engine start after the engine begins to rotate by sensingcamshaft and crankshaft positions.

Referring now to FIG. 6, a flowchart of a method for starting an engineis shown. The method of FIG. 6 may be executed via instructions in acontroller of a system such as is shown in FIG. 1.

At 602, method 600 judges whether or not there has been an automaticengine stop requested. If so, method 600 indicates yes and proceeds to604. Otherwise, method 600 indicates no and proceeds to exit. In someexamples, the method of FIG. 6 only executes when a temperature of theengine is greater than a threshold amount.

At 604, method 600 suspends spark to engine cylinders in an orderlymanner and fuel delivery to selected cylinders. In one example, deliveryof fuel to cylinders that have started receiving fuel before the enginestop request is ceased after the cylinder cycle in which the engine stoprequest occurred, with the exception of the cylinder scheduled for afirst combustion event after engine stop. Fuel delivery for cylindersnot having received fuel during the cylinder cycle when the engine stoprequest is made is ceased upon the engine stop request. Spark issuspended for cylinders that hold no air-fuel mixture and spark forcylinder holding an air-fuel mixture is ceased after the air fuelmixture is combusted (e.g., see FIGS. 2-5). Method 600 proceeds to 606after spark delivery to engine cylinder is suspended.

At 606, method 600 judges which cylinder or cylinders are scheduled toreceive fuel for the purpose of restarting the engine after engine stop.The fuel is delivered so that it may be trapped in the cylinder duringthe engine stop period. However, since the exact engine stoppingposition cannot always be anticipated while the engine is turning,alternative strategies are provided to restart the engine at 616-642.

In one example, method 600 waits until engine speed is less than athreshold and then assesses engine position. Based on the engineposition when engine speed is less than a threshold, a cylinder orcylinders are selected to receive a final fuel injection before enginestop. The fuel mixture is not ignited and spark remains deactivated. Forexample, if engine speed is less than 100 RPM and cylinder number one ispresently in an expansion stroke, cylinder number one may be selected toreceive a final fuel injection. In some examples, the engine may bestopped without providing fuel to trap in cylinders at 606. Method 600proceeds to 610 after fuel is injected to one or more cylinders topromote engine restarting after engine stop.

At 610, method 600 determines engine position at engine stop. Engineposition may be determined via reading teeth of a wheel that rotateswith the engine crankshaft. In some examples, the wheel position may besensed at zero engine speed. In other examples, method 600 may estimateengine stop position based on the latest available engine positioninformation before engine stop. Method 600 proceeds to 612 after engineposition is determined.

At 612, method 600 judges whether or not there is an engine restartrequest. The engine restart request may be automatically initiated via acontroller monitoring vehicle conditions such as brake pedal condition.If method 600 judges that an engine start request is present, method 600proceeds to 614. Otherwise, method 600 returns to 612.

At 614, method 600 engages the engine starter and determines engine stoptime via summing the time from engine stop to engine rotation. Method600 proceeds to 616 after engine stop time is determined. In someexamples, method 600 also starts a timer upon engine rotation to providetime since engine stop.

At 616, method 600 judges whether or not the intake valve of thecylinder having received fuel for a first combustion event at restartduring the engine stop procedure is open or closed. If the intake valveis open, method 600 proceeds to 618. Otherwise, the intake valve isdetermined to be closed and method 600 proceeds to 630.

At 618, method 600 judges whether or not the remaining opening durationof the intake valve of the cylinder having received fuel for a firstcombustion event at restart during the engine stop procedure is greaterthan a threshold amount and if the engine stop time has exceeded athreshold amount of time. For example, if the intake valve openingduration of the cylinder that received fuel for a first combustion eventat restart during the engine stop procedure is greater than 30crankshaft degrees and the engine has stopped for four minutes, method600 proceeds to 620. Otherwise, method 600 proceeds to 640. When thevalve opening duration is greater than a threshold amount and the enginehas been stopped for more than a threshold amount of time, it may bedetermined that the injected fuel can enter the cylinder and that atleast a portion of fuel injected during the engine stop procedure mayhave exited the cylinder via the open intake valve.

At 620, method 600 injects fuel to the cylinder having received fuel fora first combustion event at restart during the engine stop procedure. Inother words, the cylinder scheduled for a first combustion event atengine restart receives two injections of fuel. A first fuel injectionduring the engine stop procedure and a second fuel injection during theengine restart. In one example, the second amount of fuel injected tothe cylinder is based on time that the engine is stopped and enginetemperature. Method 600 proceeds to 622 after fuel is injected to thecylinder.

At 622, method 600 begins to rotate the engine via a starter. Thestarter may be automatically or manually engaged. In some examples, 620may occur after 622. Method 600 proceeds to 624.

At 624, method 600 provides a spark to the cylinder having received fuelfor a first combustion event at restart during the engine stopprocedure. The spark initiates the air-fuel mixture and provides a firstcombustion event since engine stop. Method 600 proceeds to 626 afterspark is provided. In other examples, fuel may be injected to otherengine cylinders before spark is provided to the cylinder havingreceived fuel for a first combustion event at restart during the enginestop procedure to maintain combustion in firing order of the engine.

At 626, method 600 injects fuel sequentially to cylinders in the orderof combustion of the engine. However, as illustrated in FIG. 2-5 someengine cylinders may receive fuel substantially simultaneously so thatorder of combustion may be maintained. For example, one cylinder mayreceive fuel at a time its intake valve is open (e.g., during an intakeor compression stroke) while another cylinder receives fuel when itsintake valve is closed (e.g., during an exhaust stroke). In one example,two cylinders receive fuel injected during an open intake valve time(e.g., cylinders providing the first and second combustion events sinceengine stop). The remaining cylinders receive fuel injected duringclosed intake valve timings of the respective cylinders (e.g., see FIG.2). Method 600 proceeds to 628 after fuel is injected.

At 628, method 600 provides spark during each cylinder cycle to enginecylinders receiving fuel. The spark may be provided during compressionor expansion strokes of the respective cylinders (e.g., see FIG. 2 aftertime T₄). Spark is provided sequentially after fuel is injected toengine cylinders. Method 600 exits after spark delivery to enginecylinders begins.

At 640, method 600 injects fuel to a cylinder next in combustion orderfrom the cylinder having received fuel for a first combustion event atrestart during the engine stop procedure. For example, a four cylinderengine having a firing order of 1-3-4-2 as shown in FIG. 3, wherecylinder number one receives fuel during an engine stop procedure,cylinder number three is the first cylinder to receive fuel injection inresponse to an engine start request. Fuel is injected to cylinder numberthree because the opening duration of the intake valve of cylindernumber one is determined to be too short for the cylinder number one toreceive the injected fuel. Therefore, injection of additional fuel tocylinder number one is omitted. In this way, the cylinder does notinduct excess fuel during a subsequent intake event. Method 600 proceedsto 642 after fuel is injected to the engine.

At 642, method 600 provides spark to the cylinder next in combustionorder from the cylinder having received fuel for a first combustionevent at restart during the engine stop procedure. However, in someexamples, method 600 may provide spark to both the cylinder havingreceived fuel for a first combustion event at restart during the enginestop procedure and the next cylinder in order of combustion. Method 600proceeds to 626.

At 630, method 600 begins to rotate the engine via a starter. Thestarter may be automatically or manually engaged. In some examples, 630may occur after 636 or 634. Method 600 proceeds to 632 after beginningengine rotation.

At 632, method 600 judges whether or not the engine stop time is greaterthan a threshold engine stop time. If so, method 600 proceeds to 636.Otherwise, method 600 proceeds to 634. If the engine stop time exceeds athreshold amount of time, air may seep out of or crankcase gases mayseep into the engine cylinder, thereby reducing cylinder pressure duringcombustion and increasing engine noise and vibration.

At 636, method 600 injects fuel to the port of a cylinder next incombustion order from the cylinder having received fuel for a firstcombustion event at restart during the engine stop procedure. Thus, asecond injection of fuel to the cylinder having received fuel for afirst combustion event at restart is omitted. Method 600 proceeds to638.

At 638, method 600 provides a first spark since engine stop to thecylinder next in combustion order from the cylinder having received fuelfor a first combustion event at restart during the engine stop procedure(e.g., see FIG. 5). Thus, the cylinder having received fuel for a firstcombustion event at restart during the engine stop procedure is not thecylinder of where the first combustion event since engine stop occurs.However, if desired, a first spark may be provided to the cylinderhaving received fuel for a first combustion event at restart during theengine stop procedure. If spark is not provided to the cylinder havingreceived fuel for a first combustion event at restart during the enginestop procedure, one or more engine cylinder air-fuel mixtures may bemade leaner during engine start to offset hydrocarbons ejected from thecylinder having received fuel during the engine stop procedure. Method600 proceeds to 626 after providing spark to the fueled cylinder.

At 634, method 600 provides spark to the cylinder having received fuelfor a first combustion event at restart during the engine stopprocedure. The spark provides an ignition source for the fuel that wastrapped in the cylinder during the engine stop period (e.g., see FIG.4). Since the air-fuel mixture is trapped in the cylinder for a shortduration, the cylinder mixture may be suitable for combustion. Method600 proceeds to 626 after spark is provided to the cylinder.

Thus, the method of FIG. 6 provides for a method for starting an engine,comprising: during an engine start and after an engine start request,selectively injecting fuel to a port of only a single engine cylinderhaving an open intake valve at a time fuel is injected to the port; andinjecting fuel to each remaining engine cylinder at times when an intakevalve of a cylinder receiving fuel is closed. The method includes whereselectively injecting fuel to the port of a single cylinder having anopen intake valve at a time fuel is injected to the port includesinjecting fuel when a remaining portion of an opening duration of theintake valve is greater than a threshold number of crankshaft degrees.The method also includes where selectively injecting fuel to the port ofa single cylinder having an open intake valve at a time fuel is injectedto the port includes not injecting fuel when the remaining portion of anopening duration of the intake valve is less than a threshold number ofcrankshaft degrees. The method further includes where the remainingportion of an opening duration of the intake valve is measured from anengine stop position to when the intake valve closes.

The method of FIG. 6 further comprising stopping the engine beforestarting the engine and supplying fuel to the single cylinder withoutcombusting the supplied fuel before the engine is stopped. In this way,the amount of time it takes to restart the engine can be reduced sinceone cylinder already contains fuel at engine start time. The methodfurther comprises where fuel is supplied to a second cylinder duringstopping the engine without combusting fuel supplied to the secondcylinder before the engine is stopped. The method includes where thesingle cylinder is a second cylinder to enter an intake stroke duringengine rotation after engine stop.

The method of FIG. 6 also includes a method for starting an engine,comprising: stopping the engine and injecting fuel to at least onecylinder without combusting the injected fuel before engine stop, theinjected fuel trapped in the at least one cylinder via closed intake andexhaust valves; during an engine start and after an engine startrequest, selectively combusting the injected fuel via supplying a sparkto the at least one cylinder of the engine. The method includes whereselectively combusting the injected fuel includes not combusting theinjected fuel in the at least one cylinder when the injected fuel istrapped in the at least one cylinder for less than a threshold amount oftime. The method also includes where selectively combusting the injectedfuel includes combusting the injected fuel in the at least one cylinderwhen the injected fuel is trapped in the at least one cylinder for morethan a threshold amount of time.

The method of FIG. 6 further comprises injecting fuel to a port of asecond cylinder of the engine at a time when an intake valve of thesecond cylinder is open, the injecting fuel to the port of the secondcylinder for a first combustion event in the second cylinder sinceengine stop. Thus, at time of engine restart, a second cylinder may beselected for a first combustion event since engine stop depending on thefinal engine stop position.

In some examples, the method further comprises injecting fuel to eachremaining cylinder of the engine at a time when an intake valve of acylinder receiving fuel is closed. A method also includes where theengine is automatically stopped and automatically started. The methodalso includes where a temperature of the engine is above a firstthreshold when selectively combusting the injected fuel via supplying aspark to the at least one cylinder of the engine, and where the engineis not stopped automatically when the temperature of the engine is lessthan a second threshold temperature.

The method of FIG. 6 also provides for an engine with cylinders,comprising: stopping the engine while injecting and trapping fuel in afirst cylinder without combusting the injected fuel; and during asubsequent engine start: combusting the trapped fuel via supplying aspark; port injecting fuel to only a second cylinder during an openintake valve; and port injecting fuel to each remaining engine cylinderduring a closed intake valve.

As will be appreciated by one of ordinary skill in the art, methoddescribed in FIG. 6 may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the objects, features, andadvantages described herein, but is provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas,gasoline, diesel, or alternative fuel configurations could use thepresent description to advantage.

The invention claimed is:
 1. A method for starting an engine,comprising: during an engine start and after an engine start request,selectively injecting fuel to a port of only a single engine cylinderhaving an open intake valve at a time fuel is injected to the port; andinjecting fuel to each remaining engine cylinder at times when an intakevalve of a cylinder receiving fuel is closed, the single cylinder beinga second cylinder to enter an intake stroke during engine rotation afterengine stop.
 2. The method of claim 1, where selectively injecting fuelto the port of a single cylinder having an open intake valve at a timefuel is injected to the port includes injecting fuel when a remainingportion of an opening duration of the intake valve is greater than athreshold number of crankshaft degrees.
 3. The method of claim 2, whereselectively injecting fuel to the port of a single cylinder having anopen intake valve at a time fuel is injected to the port includes notinjecting fuel when the remaining portion of an opening duration of theintake valve is less than a threshold number of crankshaft degrees. 4.The method of claim 3, where the remaining portion of an openingduration of the intake valve is measured from an engine stop position towhen the intake valve closes.
 5. The method of claim 1, furthercomprising stopping the engine before starting the engine and supplyingfuel to the single cylinder without combusting supplied fuel before theengine is stopped.
 6. The method of claim 5, further comprising wherefuel is supplied to a second cylinder during stopping the engine withoutcombusting fuel supplied to the second cylinder before the engine isstopped.
 7. A starting method for an engine with cylinders, comprising:stopping the engine while injecting and trapping fuel in a firstcylinder without combusting the injected fuel; and during a subsequentengine start: combusting the trapped fuel via supplying a spark; portinjecting fuel to only a second cylinder during an open intake valve;and port injecting fuel to each remaining engine cylinder sequentiallyin order of combustion during a closed intake valve.
 8. A method forstarting an engine, comprising: during an engine start and after anengine start request, selectively injecting fuel to a port of only asingle engine cylinder having an open intake valve at a time fuel isinjected to the port; injecting fuel to each remaining engine cylinderat times when an intake valve of a cylinder receiving fuel is closed;and stopping the engine before starting the engine and supplying fuel tothe single cylinder without combusting the supplied fuel before theengine is stopped.
 9. The method of claim 8, where selectively injectingfuel to the port of a single cylinder having an open intake valve at atime fuel is injected to the port includes injecting fuel when aremaining portion of an opening duration of the intake valve is greaterthan a threshold number of crankshaft degrees.
 10. The method of claim9, where selectively injecting fuel to the port of a single cylinderhaving an open intake valve at a time fuel is injected to the portincludes not injecting fuel when the remaining portion of an openingduration of the intake valve is less than a threshold number ofcrankshaft degrees.
 11. The method of claim 10, where the remainingportion of an opening duration of the intake valve is measured from anengine stop position to when the intake valve closes.
 12. The method ofclaim 8, further comprising where fuel is supplied to a second cylinderduring stopping the engine without combusting fuel supplied to thesecond cylinder before the engine is stopped.
 13. The method of claim 8,where the single cylinder is a second cylinder to enter an intake strokeduring engine rotation after engine stop.